The Multifaceted Reactivity of Single‐Atom Heterogeneous Catalysts

Abstract

Single-atom heterogeneous catalysts (SACs) attached to carefully chosen hosts are attracting considerable interest; principally because they offer maximum utilization per metal atom and are usually readily recyclable. However, diminution of the atomic population of nanoparticles or nanoclusters to single atoms can significantly alter reactivity because of the consequent changes in the active-site structure. By examining various diverse applications, we ascertain whether the performance of SACs is enhanced or suppressed. We also note that SACs generally display unique kinds of catalytic cycles. The choice of host is crucial since it influences both the electronic and steric environment of the metal center. Moreover, it may function as a cocatalyst. All these aspects impact upon the design of new SACs, which exhibit similarities to hetero- and homogeneous predecessors. Additionally, SACs offer a viable replacement of soluble metal complexes in processes that remain difficult to heterogenize.

One‐Pot Cooperation of Single‐Atom Rh and Ru Solid Catalysts for a Selective Tandem Olefin Isomerization‐Hydrosilylation Process

“…[1] Often referred to as single-atom catalysts (SACs), these materials hold the potential to achieve aq uantitative surface exposure of the supported metal for catalysis while displaying ah igher site structural homogeneity -which is expected to translate into superior catalytic selectivitycompared to supported catalysts based on metal (oxide) clusters or nanoparticles.A tomically dispersed supported metals often exist in acationic state,astheir full reduction to azero-valent state implies that bonds to the oxide support are cleaved, which is typically followed by high adatom surface mobility and agglomeration even at relatively mild temperatures. [2] Their cationic nature,m onoatomicity and defined coordination environment make oxide-supported SACs excellent candidates to bridge the gap between the disciplines of heterogeneous and homogeneous catalysis, [3] particularly in an umber of areas which have been traditionally dominated by molecular complex catalysts applied in solution. Hence, SACs have been recently explored for reactions classically catalyzed by cationic metal salts or complexes,i ncluding olefin hydroformylation, [5] olefin hydrosilylation, [6] alkyne hydrochlorination, [7] or C À Ccoupling.…”

Tailoring Nitrogen‐Doped Carbons as Hosts for Single‐Atom Catalysts

“…Furthermore, to ensure high performance in targeted reactions the strength of interaction of the metal with the host should be optimized since this determines its electronic properties. In this context, hosts with well‐defined surface functional groups and tunable properties offer great potential . Graphitic carbon nitride (C 3 N 4 ) has proven an effective host to stabilize various single metal atoms due to the six‐fold nitrogen coordination sites intrinsic to its structure .…”

Single-Atom Catalysis: How Structure Influences Catalytic Performance

“…The charged metal centre bound to surface atoms has seen SAC systems likened to the organometallic complexes utilized in homogeneous catalysis.Figure adapted from Ref. [18] …”